Field of the Invention
The present disclosure relates to an active front steering (AFS) system for a vehicle. More particularly, it relates to an AFS system for a vehicle, which is capable of easily compensating for a clearance between respective gear elements of a planetary gear set by newly improving a power transmission structure between a motor and the planetary gear set that constitute the AFS system.
Description of Related Art
An active front steering (hereinafter, referred to as AFS) system, which is applied to a steering system for a vehicle, is a system that changes a steering gear ratio for each vehicle speed, such as a high speed and a low speed, to stabilize behavior of the vehicle, and provides a fast steering gear ratio at a low speed, and a slow steering gear ratio at a high speed.
In other words, the AFS system provides a fast steering gear ratio when the vehicle travels at a low speed (e.g., when the vehicle is being parked) so that a steering operation is promptly and quickly carried out when a driver manipulates a steering wheel, and the AFS system provides a slow steering gear ratio when the vehicle travels at a medium or high speed so that the steering operation may be stably carried out by reducing steering sensitivity to the steering wheel.
To this end, the AFS system in the related art includes an input shaft which is connected with the steering wheel, a planetary gear set which reduces rotational force, which is transmitted from the input shaft, with a predetermined gear ratio, and a motor which is connected to one of gear elements of the planetary gear set by means of a worm and a worm wheel so that the motor may transmit power.
However, the AFS system in the related art requires components, such as the worm and the worm wheel, for transmitting power from the motor, in addition to essential components such as the planetary gear set and the motor, and as a result, there is a problem in that the structure of the AFS system is complicated, and the number of components is increased.
Meanwhile, there are clearances between the respective gear elements of the planetary gear set that is applied to the AFS system, for example, clearances between a sun gear and planet gears, and clearances between the planet gears and a ring gear, which causes vibration and noise.
Therefore, in order to reduce the clearances between the respective gear elements of the planetary gear set, a method of tightly maintaining, by using springs or the like, center distances between the respective gear elements, for example, center distances between the sun gear and the planet gears or between the planet gears and the ring gear is applied. However, there are problems in that even in a case in which shafts of the respective gear elements are slightly misaligned, engagement between teeth of the gear elements is broken, and the teeth of the respective gear elements do not properly mesh with each other, such that the teeth of the gear elements are caught.
Accordingly, there is a need for a new method of compensating for the clearances between the respective gear elements that constitute the AFS system, and there is also a need for a method of more simply transmitting power between the planetary gear set and the motor.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.